The invention relates to a bone anchoring device for anchoring a stabilization rod in a bone or in a vertebra. The bone anchoring device includes an anchoring element and a receiving part for receiving a head of the bone anchoring element and for receiving a stabilization rod to be connected to the anchoring element. The anchoring element is pivotably connected to the receiving part and can be fixed at an angle by exerting pressure onto the head via a pressure element that is arranged in the receiving part. The pressure element and the receiving part have recesses and projections that are configured to cooperate in such a way that the pressure element can assume a position within the receiving part in which it clamps the head by friction without locking it.
U.S. Pat. No. 5,716,356 describes a polyaxial bone screw including a screw element, a receiving part that is pivotably connected to the screw element, and a pressure element to exert pressure onto the head of the screw element to fix the angle between the screw element and the receiving part. The receiving part has a U-shaped channel for receiving a stabilization rod. The pressure element comprises a cylindrical recess that is to be aligned with the U-shaped channel to receive the rod therein. In order to hold the pressure element in a position aligned with the U-shaped channel, the position of the pressure element is fixed by crimping through bores provided in the receiving part.
U.S. Pat. No. 5,672,176 describes another example of a polyaxial bone screw with a pressure element that is also held in place by crimp bores without impeding a sufficient movement of the pressure element to clamp the head. The receiving part has a tapering inner surface portion and the pressure element has a correspondingly tapering outer surface in a region laterally surrounding said screw head. By the cooperating tapering surfaces, the head can be locked while still allowing adjustments of the position of the rod.
WO 2006/116437 A2 describes a bone anchor for spinal fixation in the form of a polyaxial bone screw including screw element, a housing, a sleeve and a collet arranged in the housing for exerting pressure onto the head of the screw element. The sleeve has retention tabs that snap into slots in opposite wall portions of the housing.
If the head of the anchoring element is freely pivotable with respect to the receiving part, the alignment of the receiving part and the insertion of the rod may be difficult in more complex clinical applications, for example, when a multitude of bone anchors have to be connected to the rod.
U.S. Pat. No. 7,604,656 describes a fastener engageable with a bone portion to connect a longitudinal member to the bone portion. The housing that receives the fastener also receives a spacer that is engageable with the fastener and the longitudinal member. In one embodiment the spacer is urged by a pin member into frictional engagement with the fastener and with the housing.